The principal figure of merit used to characterize a sensor is its sensitivity (S), defined asS=ΔI/I0 
where I0 is the current flowing through the sensor and ΔI the current variation due to a sensing event.
Nano-scale devices typically function with currents in the nA range. Sophisticated measurement setups are thus needed to discriminate variations in conductivity of only a few percents and minimize other sources of noise that could overshadow detection events (light, vibrations, thermal drift, etc.).